A large stone is pushed onto a lorry by means of a ramp. The ramp has length $l$. The stone is raised through a height of $h$. The stone has mass $m$. Its weight is $W$. Which expression is equal to the useful work done on the stone?
- A$m \times h$
- B$W \times h$
- C$m \times l$
- D$W \times l$